Neural transplantation in Parkinson's disease.

Transplanted human embryonic dopamine neurons reinnervate the striatum in patients with Parkinson's disease. The grafts can exhibit long-term survival without immunological rejection and despite an ongoing disease process and continuous antiparkinsonian drug treatment. Recent findings using positron emission tomography indicate that the grafts are functionally integrated in the patient's brain and release dopamine into the striatum. In the most successful cases, patients have been able to withdraw L-dopa treatment after transplantation and resume an independent life. About two-thirds of grafted patients have shown clinically useful, partial recovery of motor function: increased percentage of time in the 'on'-phase and reduced rigidity and hypokinesia during 'off'-phases, bilaterally but predominantly on the side contralateral to the graft. Gait, speed, balance and dyskinesias have not exhibited any major, consistent improvements. Current research aims at solving three main problems: (a) large amounts of human embryonic mesencephalic tissue are needed for therapeutic effects; (b) symptomatic relief is incomplete and varies between patients; and (c) patient selection and grafting procedure have not been optimized.